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62 lines
2.7 KiB
62 lines
2.7 KiB
.. _tutorial-dbcon: |
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Step 4: Request Database Connections |
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------------------------------------ |
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Now we know how we can open database connections and use them for scripts, |
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but how can we elegantly do that for requests? We will need the database |
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connection in all our functions so it makes sense to initialize them |
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before each request and shut them down afterwards. |
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Flask allows us to do that with the :meth:`~flask.Flask.before_request`, |
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:meth:`~flask.Flask.after_request` and :meth:`~flask.Flask.teardown_request` |
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decorators:: |
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@app.before_request |
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def before_request(): |
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g.db = connect_db() |
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@app.teardown_request |
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def teardown_request(exception): |
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db = getattr(g, 'db', None) |
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if db is not None: |
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db.close() |
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Functions marked with :meth:`~flask.Flask.before_request` are called before |
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a request and passed no arguments. Functions marked with |
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:meth:`~flask.Flask.after_request` are called after a request and |
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passed the response that will be sent to the client. They have to return |
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that response object or a different one. They are however not guaranteed |
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to be executed if an exception is raised, this is where functions marked with |
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:meth:`~flask.Flask.teardown_request` come in. They get called after the |
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response has been constructed. They are not allowed to modify the request, and |
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their return values are ignored. If an exception occurred while the request was |
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being processed, it is passed to each function; otherwise, `None` is passed in. |
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We store our current database connection on the special :data:`~flask.g` |
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object that Flask provides for us. This object stores information for one |
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request only and is available from within each function. Never store such |
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things on other objects because this would not work with threaded |
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environments. That special :data:`~flask.g` object does some magic behind |
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the scenes to ensure it does the right thing. |
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For an even better way to handle such resources see the :ref:`sqlite3` |
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documentation. |
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Continue to :ref:`tutorial-views`. |
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.. hint:: Where do I put this code? |
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If you've been following along in this tutorial, you might be wondering |
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where to put the code from this step and the next. A logical place is to |
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group these module-level functions together, and put your new |
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``before_request`` and ``teardown_request`` functions below your existing |
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``init_db`` function (following the tutorial line-by-line). |
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If you need a moment to find your bearings, take a look at how the `example |
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source`_ is organized. In Flask, you can put all of your application code |
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into a single Python module. You don't have to, and if your app :ref:`grows |
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larger <larger-applications>`, it's a good idea not to. |
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.. _example source: |
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http://github.com/mitsuhiko/flask/tree/master/examples/flaskr/
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